What key factor prevented NASA from authorizing an immediate Starliner return attempt during troubleshooting?

They needed high confidence in the vehicle's ability to perform its departure sequence reliably

NASA’s decision-making process explicitly prioritized thoroughness and safety over adhering strictly to the original schedule when dealing with the propulsion anomalies. Officials repeatedly stressed that no return attempt would be authorized until they possessed high confidence in Starliner's ability to successfully execute its departure sequence, which includes undocking, deorbit burn, and course corrections. This cautious approach acknowledged that the margin for error in human spaceflight is essentially zero, requiring iterative problem-solving on orbit to bridge the gap between the vehicle's *capability* to remain in orbit and the *confidence* required for safe return maneuvers.